This invention generally relates to a power conserving arrangement for, and method of, minimizing battery power consumption during stand-by operation of a portable, battery-operated, mobile device and, more particularly, a wireless telephone system.
A typical cellular telephone communicates with a base station, the base station transmitting messages to the cellular telephone on a regular basis. Similarly, a cordless telephone communicates with the base unit and remains ready to respond to any incoming call. These telephones usually include some form of a transceiver and a decoder under microprocessor control.
During a standby mode of operation, the telephone waits to receive a telephone call through the base unit. During the stand-by mode of operation, the telephone continuously receives and decodes all messages transmitted by the base unit and synchronizes itself with the base unit regularly. The telephone consumes electrical power in both the talk and the standby modes. In cordless battery-operated telephones, the on-board battery typically has a working lifetime of approximately 100 hours in the stand-by mode and about 10 hours in the talk mode (in the DECT standard as an example). The battery is then re-charged or replaced to continue telephone service. The microprocessor and other electronic components onboard the telephone are energized during the standby mode which contributes to current drain on the battery. The need to increase the battery lifetime between re-charges and/or battery replacement is self-evident.
Cordless telephones, while in an idle or standby mode, constantly monitor a continuous stream of signals sent by the base unit. Typically, the cordless telephone uses a dotting sequence, the first segment of the message to synchronize the telephone hardware to a master clock frequency in the base. The portable unit or handset (cordless or cellular) needs to be synchronized with the base station and transmitted signal to allow for accurate and reliable communication.
In order to preserve power of the battery in the handset, the receiver portion or the handset moves into an idle locked mode or standby mode waiting for an actual call to come in. The handset typically powers down during the standby mode but the internal communication circuits need to remain in synchronization with the base station signal, thereby consuming battery power. It would be commercially advantageous to provide a method and an apparatus for reducing power consumption during the standby mode without increasing cost or hardware complexity.
The present invention is exemplified in a number of implementations and applications, some of which are summarized below. One of the advantages of the present invention is the ease of incorporation of the method into existing wireless telephones without significant hardware or software redesign. Accordingly, a method is described herein that addresses this need of reducing power consumed by a receiver of a communications device. In an example embodiment, the receiver has an internal power source and a corresponding base unit. The receiver of the communications device is adapted to receive a transmitted signal in the form of a data stream, the data stream defined by a plurality of frames, each of the frames including a synchronization sub-frame. The method includes detecting the activity status of the receiver with respect to the transmitted signal, the receiver being in an idle state when not receiving a transmitted signal. The idle state is defined by a predetermined number of frames that include a set of active state frames and inactive state frames that combine to defined a duration of the idle state. A clock signal is generated that has an output frequency that varies as a function of the active and inactive frames. The clock frequency is higher in the active state and lower in the inactive state, such that the receiver consumes more power during the active state then when in the inactive state. The receiver is then synchronized with the sub-frame of the transmitted signal during the idle state. Power consumed by the receiver is then reduced by reducing the clock frequency as the number of inactive frames within the idle state are increased. In the present invention, the power consumed by the receiver is a function of the power consumed during the active and inactive states and the duration of the idle state.
According to another aspect of the invention, a method is directed to reducing power consumption of a receiver of a communications device during an idle state mode. The receiver has an internal power source and a corresponding base unit. The receiver of the communications device is adapted to receive a transmitted signal in the form of a data stream defined by a plurality of frames. The idle state is defined by a predetermined number of frames that include a set of active state frames and inactive state frames that combined to define a duration of the idle state. The method includes generating a clock signal that has an output frequency that varies as a function of the active and inactive frames. The clock frequency is higher in the active state and lower in the inactive state, such that the receiver consumes more power during the active state then when in the inactive state. The receiver is then synchronized with the sub-frame of the transmitted signal during the idle state. The power consumed by the receiver is then reduced by dynamically and synchronously switching the clock frequency to a lower clock frequency. The lower clock frequency corresponds to the inactive state and the increased number of inactive frames within the idle state. The power consumed by the receiver is a function of the power consumed during the active and inactive states and the duration of the idle state.
In yet another aspect of the invention, a system for reducing power consumption of a receiver of a communications device is described. The receiver has an internal power source and a corresponding base unit. The receiver is adapted to receive a transmitted signal in the form of a data stream, the data stream defined by a plurality of frames, each of the frames including a synchronization sub-frame. The system includes a detector adapted to detect the activity status of the receiver with respect to the transmitted signal. The receiver is in an idle state when not receiving a transmitted signal, the idle state defined by a predetermined number of frames that include a set of active state frames and inactive state frames that combined define a duration of the idle state. A clock signal generator coupled to the detector generates a clock signal with an output frequency that varies as a function of the active and inactive frames. The clock frequency is higher in the active state and lower in the inactive state, such that the receiver consumes more power during the active state then when in the inactive state. Synchronizing circuitry, coupled to the receiver and the clock signal generator, synchronizes the receiver with the sub-frame of the transmitted signal during the idle state and reduces the power consumed by the receiver. The power consumed by the receiver is reduced by reducing the clock frequency by increasing the number of inactive frames within the idle state. The power consumed by the receiver is a function of the power consumed during the active and inactive states and the duration of the idle state.
In yet another aspect of the invention, an apparatus is directed to reducing power consumption of a receiver of a communications device during an idle state. The receiver has an internal power source and a corresponding base unit. The receiver is adapted to receive a transmitted signal in the form of a data stream defined by a plurality of frames. The idle state is defined by a predetermined number of frames that include a set of active state frames and inactive state frames that combine to define a duration of the idle state. The apparatus includes a clock signal generator that has an output frequency that varies as a function of the active and inactive frames. The clock frequency is higher in the active state and lower in the inactive state, such that the receiver consumes more power during the active state then when in the inactive state. The apparatus further includes circuitry for synchronizing the receiver with the transmitted signal during the idle state, the circuitry coupled to the receiver and the clock signal generator. The apparatus also includes a mechanism adapted to reduce the power consumed by the receiver that is coupled to the clock generator. The mechanism dynamically and synchronously switches the clock frequency to a lower clock frequency corresponding to the inactive state that has an increased number of inactive frames within the idle state. The power consumed by the receiver is a function of the power consumed during the active and inactive states and the duration of the idle state.
The above summary is not intended to provide an overview of all aspects of the present invention. Other aspects of the present invention are exemplified and described in connection with the detailed description.